* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Kroenke-DBP-e10-PPT-Chapter12
Survey
Document related concepts
Microsoft Access wikipedia , lookup
Oracle Database wikipedia , lookup
Extensible Storage Engine wikipedia , lookup
Entity–attribute–value model wikipedia , lookup
Ingres (database) wikipedia , lookup
Concurrency control wikipedia , lookup
Navitaire Inc v Easyjet Airline Co. and BulletProof Technologies, Inc. wikipedia , lookup
Functional Database Model wikipedia , lookup
Microsoft SQL Server wikipedia , lookup
Microsoft Jet Database Engine wikipedia , lookup
ContactPoint wikipedia , lookup
Relational model wikipedia , lookup
Clusterpoint wikipedia , lookup
Transcript
COS 236 Day 22 DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-1 Agenda • Assignment 9 Posted – Due Today • Assignment 10 Posted – Due April 26 – 1 (2?) more to go • Last Capstone Progress Reports Due April 26 • Today we will discuss – OBDC, OLE DB, ADO and ASP DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-2 End of days? (subject to change) • April 23 – DP Chap 12 – SQL Chap 11 – Assignment 9 due • April 26 – DP Chapter 13 – Assignment 10 due • April 30 – DP Chap 14 • May 3 – DP Chap 15 – Review – Assignment 11 Due • May 9 – Quiz 3 – 10 AM – Capstone presentations DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-3 David M. Kroenke’s Database Processing: Fundamentals, Design, and Implementation Chapter Twelve: ODBC, OLE DB, ADO, and ASP Part One DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-4 Introduction • Because database applications today reside in a complicated environment, various standards have been developed for accessing database servers. • Some of the important standards are – OBDC (Open Database Connectivity) is the early standard for relational databases. – OLE DB is Microsoft’s object-oriented interface for relational and other databases. – ADO (Active Data Objects) is Microsoft’s standard providing easier access to OLE DB data for the non-object-oriented programmer. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-5 The Web Server Data Environment • A Web server needs to publish applications that involve different data types. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-6 The Role of the ODBC Standard DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-7 The Role of ODE DB DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-8 The Role of ADO DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-9 Open Database Connectivity (OBDC) • The Open Database Connectivity (ODBC) standard provides a DBMS-independent means for processing relational database data. • It was developed in the early 1990s by an industry committee and has been implemented by Microsoft and many other vendors. • The goal is to allow a developer to create a single application that can access databases supported by different DBMS products without needing to be changed or recompiled. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-10 ODBC Architecture DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-11 OBDC Components (Continued) • OBDC consists of a data source, an application program, a driver manager, and a DBMS driver. • A data source is the database and its associated DBMS, operating system, and network platform. – An ODBC data source can be a relational database, a file server, or a spreadsheet. • An applications program issues requests to create a connection with a data source. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-12 OBDC Components • A driver manager determines the type of DBMS for a given ODBC data source and loads that driver in memory. • A DBMS driver processes ODBC requests and submits specific SQL statements to a given type of data source. – A single-tier driver processes both ODBC calls and SQL statements. – A multiple-tier driver processes ODBC calls, but passes the SQL requests to the database server. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-13 ODBC Driver Types: ODBC Single-Tier Driver DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-14 ODBC Driver Types: ODBC Multiple-Tier Driver DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-15 Conformance Levels • Levels of conformance balance the scope of the OBDC standard. • There are two types of conformance levels: – ODBC conformance levels concern the features and functions that are made available through the driver’s application program interface (API). • A driver API is a set of functions that the application can call to receive services. – SQL conformance levels specify which SQL statements, expressions, and data types a driver can process. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-16 Summary of OBDC Conformance Levels DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-17 Summary of OBDC Conformance Levels (Continued) DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-18 Summary of SQL Conformance Levels DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-19 Summary of SQL Conformance Levels (Continued) DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-20 ODBC Data Sources • A data source is an ODBC data structure that identifies a database and the DBMS that processes it. • Three types of data source names: – A file data source is a file that can be shared among database users having the same DBMS driver and privilege. – A system data source is local to a single computer and may be used by the operating system and any user on that system. • System data sources are recommended for Web servers. • To define a system data source name, the type of driver and the database need to be specified. – A user data source is available only to the user who created it. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-21 Creating a System Data Source: Selecting the Oracle Driver DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-22 Creating a System Data Source: Setting Data Source Properties DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-23 David M. Kroenke’s Database Processing Fundamentals, Design, and Implementation (10th Edition) End of Presentation: Chapter Twelve Part One DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-24 David M. Kroenke’s Database Processing: Fundamentals, Design, and Implementation Chapter Twelve: ODBC, OLE DB, ADO, and ASP Part Two DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-25 OLE DB • OLE DB is an implementation of the Microsoft OLE object standard. – OLE DB objects are COM objects and support all required interfaces for such objects. • OLE DB breaks the features and functions of a DBMS into COM objects, making it easier for vendors to implement portions of functionality. – This characteristic overcomes a major disadvantage of ODBC. – With ODBC, a vendor must create an ODBC driver for almost all DBMS features and functions in order to participate in ODBC at all. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-26 Object-Oriented Concepts • An object-oriented programming object is an abstraction that is defined by its properties and methods. – An abstraction is a generalization of something. – A property specifies set of characteristics of an object. – A method refers to actions that an object can perform. – A collection is an object that contains a group of other objects. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-27 OLE DB Goals • Create object interfaces for DBMS functionality pieces: – Query, update, transaction management, etc. • Increase flexibility: – – – – Allow data consumers to use only the objects they need. Allow data providers to expose pieces of DBMS functionality. Providers can deliver functionality in multiple interfaces. Interfaces are standardized and extensible. • Provide object interfaces over any type of data: – Relational and non-relational database, ODBC or native, VSAM and other files, Email, etc. • Do not force data to be converted or moved from where it is. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-28 OLE DB Basic Constructs • There are data consumers and data providers: – Data consumers - Users of OLE DB functionality. – Data providers - Sources of OLE DB functionality. • An interface is a set of objects and the properties and methods they expose in that interface: – Objects may expose different properties and methods in different interfaces. • An implementation is how an object accomplishes its tasks: – Implementations are hidden from the outside world and may be changed without impacting the users of the objects. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-29 OLE DB Terminology: Data Providers • A rowset is equivalent to a cursor. • OLE DB has two types of data providers: – Tabular data provider — exposes data via rowsets. • Examples: DBMS, spreadsheets, ISAMs, email. – Service provider — a transformer of data through OLE DB interfaces. • It is both a consumer and a provider of transformed data. • Examples: query processors, XML document creator. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-30 Rowset Interfaces DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-31 Active Data Objects (ADO) • Active Data Objects (ADO) characteristics: – A simple object model for OLE DB data consumers – It can be used from VBScript, JScript, Visual Basic, Java, C#, C++ – It is a single Microsoft data access standard – Data access objects are the same for all types of OLE DB data DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-32 Invoking ADO from Active Server Pages • In Microsoft’s Active Server Pages (ASP) are Web pages where: – Statements are enclosed within the characters <% . . .%>. – ASP statements are processed on the Web server. – Other (HTML) statements are processed by the client Web browser. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-33 The ADO Object Model DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-34 Connection Object • A connection object establishes a connection to a data provider and data source. – Connections have an isolation mode. • Once a connection is created, it can be used to create RecordSet and Command objects. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-35 RecordSet Objects • RecordSet objects represent cursors: – They have both CursorType and LockType properties. – RecordSets can be created with SQL statements. – The Fields collection of a RecordSet can be processed to individually manipulate fields. – The Errors collection contains one or more error messages that result from an ADO operation. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-36 Command Object • The command object is used to execute stored parameterized queries or stored procedures: – Input data can be sent to the correct ASP using the HTML FORM tag. – Table updates are made using the RecordSet Update method. DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-37 ADO Constants: Isolation Levels DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-38 ADO Constants: Cursor Levels DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-39 ADO Constants: Lock Types DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-40 Connection Object: ASP Code <% Dim objConn Set objConn = Server.CreateObject (“ADODB.connection”) objConn.IsolationLevel = adXactReadCommitted ‘ use ADOVBS objConn.Open “ViewRidgeSS”, %> <!--#include virtual =“ADOExamples/ADOVBS.inc --> <% objConn.Open “DSN=ViewRidgeOracle2;UID=DK1;PWD=Sesame” %> DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-41 RecordSet Object: ASP Code <% Dim objRecordSet, varSql varSQL = “SELECT * FROM ARTIST” Set objRecordSet = Server.CreateObject(“ADODB.Recordset”) objRecordSet.CursorTye = adOpenStatic objRecordSet.LockType = adLockReadOnly objRecordSet.Open varSQL, objConn %> DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-42 Fields Collection: ASP Code <% Dim varI, varNumCols, objField varNumCols = objRecordSet.Fields.Count For varI = 0 to varNumCols - 1 Set objField = objRecordSet.Fields(varI) ‘ objField.Name now has the name of the field ‘ objField.Value now has the value of the field ‘ can do something with them here Next >% DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-43 Errors Collection: ASP Code <% Dim varI, varErrorCount, objError On Error Resume Next varErrorCount = objConn.Errors.Count If varErrorCount > 0 Then For varI = 0 to varErrorCount - 1 Set objError = objConn.Errors(varI) ‘ objError.Description contains ‘ a description of the error Next End If >% DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-44 Command Object: ASP Code <% Dim objCommand, objParam, objRs ‘Create the Command object, connect it to objConn and set its format Set objCommand = Server.CreateObject(“ADODB.command”) Set objCommand.ActiveConnection = objConn objCommand.CommandText=“{call FindArtist (?)}” ‘Set up the parameter with the necessary value Set objParam = objCommand.CreateParameter (“Nationality”, adChar, adParamInput, 25) objCommand.Parameters.Append objParam objParam.Value = “Spanish” ‘Fire the Stored Proc Set objRs = objCommand.Execute >% DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-45 ADO Example: Reading a Table Artist.asp DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-46 ADO Example: Reading a Table The Artist.asp Results DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-47 David M. Kroenke’s Database Processing Fundamentals, Design, and Implementation (10th Edition) End of Presentation: Chapter Twelve Part Two DAVID M. KROENKE’S DATABASE PROCESSING, 10th Edition © 2006 Pearson Prentice Hall 12-48 CHAPTER 11: EMBEDDED SQL Copyright 2004 Prentice Hall, Inc. 11-49 EMBEDDED SQL • • Structured Query Language can be used in conjunction with many different procedural and object-oriented programming host languages. This approach to programming is termed embedded SQL, and simply means that the host language includes the ability to use SQL statements to both retrieve and store records in a non-procedural fashion. Copyright 2004 Prentice Hall, Inc. 11-50 Embedding SQL in Visual Basic 6.0 • • • Database processing is primarily accomplished through use of the ActiveX Data Objects (ADO) control. This specialized control enables a computer programmer to connect an application program written in Visual Basic to an existing database. It is easy to create the database connection. Copyright 2004 Prentice Hall, Inc. 11-51 Figure 11.1 shows an example employee processing form with an ADO control. Copyright 2004 Prentice Hall, Inc. 11-52 ADO Control • • • • • The ADO control is used to process employee records. The employee processing form displays a subset of the data columns from the employee table. The ADO control provides First, Previous, Next, and Last buttons (arrows) to make it easy to navigate from one row of data to the next. When one of the ADO control navigation buttons is clicked, the form display updates to a new record. The ADO control also has properties that can be visually programmed to make a database connection. Copyright 2004 Prentice Hall, Inc. 11-53 ADO Control • • • The ConnectionString property stores a character string that specifies how to connect to a database. Part of the ConnectionString information specifies where the database is located. The ConnectionString also specifies the type of database as well as information about provider software that is used to make a database connection. In the coding segment shown in the following VB6 Example, a connection is made to an Oracle database named Company. • • REM VB6 Example ConnectionString = "Provider=MSDAORA.1; User ID=dbock; Password=mypassword; Data Source=Company; Persist Security Info=True" (Note: All of the above code will be entered on a single coding line.) Copyright 2004 Prentice Hall, Inc. 11-54 ADO Control • • • • The CommandType property specifies how data will be retrieved from a database. Data rows are retrieved from disk and stored in a memory object called a recordset. The RecordSource property stores the actual SQL statement used to create a recordset. The records displayed for the recordset in Figure 11.1 were retrieved with the SELECT statement shown in VB6 Example 11.2. • • REM VB6 Example 11.2 SELECT emp_last_name, emp_first_name, emp_middle_name, emp_ssn, emp_address, emp_city, emp_state, emp_zip FROM employee WHERE emp_zip = '62025'; Copyright 2004 Prentice Hall, Inc. 11-55 ADO Control • • There are two additional properties for each textbox control that must be set in order for a Visual Basic form to display database data. These are the DataField and DataSource properties shown in Figure 11.2 that displays a Visual Basic property window that is associated with the textbox control that displays the employee first name. Copyright 2004 Prentice Hall, Inc. 11-56 ADO Control • • • • • The DataSource property of each textbox is set to the name of the ADO control. Here the ADO control is named adoEmployee. Setting the DataSource property of a textbox links the textbox control to the ADO control. DataField property is set to the appropriate column name from the employee table in order to specify the exact value to display in a textbox. Each textbox on the employee processing form will have the same value for the DataSource property, but the DataField property for each textbox will reflect the column of data to be displayed in that particular textbox. Copyright 2004 Prentice Hall, Inc. 11-57 Selecting Data Specified by a User Inputted Value • • • This is achieved by storing the value entered into the InputBox to a Visual Basic memory variable that stores string or character data. The Visual Basic code to produce the InputBox and store the value is shown in VB6 Example 11.4. The value entered for the social security number is stored to the strSSN variable. • • REM VB6 SQL Example 11.4 Dim strSSN As String strSSN = InputBox("Enter Employee SSN:", _ "Employee SSN Search", vbOKCancel) Copyright 2004 Prentice Hall, Inc. 11-58 Selecting Data Specified by a User Inputted Value • • The program stores the SELECT statement to a second string variable named strSQL in the code segment shown in VB6 Example 11.5. Each piece of the SELECT statement is a string of characters that are concatenated together with the Visual Basic concatenation operator (the ampersand – &). The WHERE clause has the emp_ssn column name set equal to the value stored to the strSSN variable that was captured through use of the InputBox. Copyright 2004 Prentice Hall, Inc. 11-59 Selecting Data Specified by a User Inputted Value • At execution time, the SELECT statement stored to the strSQL variable includes the social security number stored to the strSSN variable. • • • REM VB6 Example 11.5 'Store SQL statement to a string variable strSQL = "SELECT emp_last_name, emp_first_name, " & _ "emp_middle_name, emp_ssn, emp_address, " & _ "emp_city, emp_state, emp_zip" & _ "FROM employee" & _ "WHERE emp_ssn = " & strSSN Copyright 2004 Prentice Hall, Inc. 11-60 Selecting Data Specified by a User Inputted Value • • The RecordSource property of the ADO control is updated by storing the strSQL string variable to the RecordSource property as shown in VB6 Example 11.6. The ADO control is refreshed with the Refresh method. The Refresh method automatically creates a new recordset, and the correct employee row will be retrieved and displayed on the employee processing form. • • REM VB6 Example 11.6 'Update the recordset retrieved by the ADO control adoEmployee.RecordSource = strSQL adoEmployee.Refresh http://www.johnsmiley.com/cis18/Smiley017.pdf Copyright 2004 Prentice Hall, Inc. 11-61 Embedding SQL in Visual Basic.net • Visual Basic 6.0 uses the ActiveX Data Objects (ADO) approach to connect to databases through OLEDB providers (software drivers). ADO has evolved into ADO.NET in Visual Basic.NET. ADO.NET still uses OLEDB providers to connect to databases such as Oracle, Microsoft SQL Server, and Microsoft Access. The major tasks facing a database programmer are: • • – – – Connecting to a database. Executing SQL statements to add, delete, modify, or retrieve table rows. Working with datasets. Datasets replace the recordsets used in VB 6.0. Copyright 2004 Prentice Hall, Inc. 11-62 Making a Database Connection • A sample VB.NET connection string for an Oracle database named Company is shown in VB.NET Example 11.1. • • • REM VB.NET Example 11.1 strConnection = "Provider=MSDAORA.1; User ID=dbock; Password=mypassword; Data Source=Company; Persist Security Info=True" The connection string value is stored to a string constant named strConnection. VB.NET Example 11.2 shows the declaration of a connection object named objConnection. Copyright 2004 Prentice Hall, Inc. 11-63 Making a Database Connection • The value of the strConnection constant is passed to the objConnection object as an argument inside parentheses. Following this the database connection is opened by using the Open method. • • • • • • • • • • • REM VB.NET Example 11.2 Module MyConnection Private Const strConnection As String = & _ "Provider = MSDAORA.1; User ID=dbock; Password=mypassword; & _ "Data Source=Company; Persist Security Info=False" Sub Main() Dim objConnection As New _ System.Data.OleDb.OleDbConnection(strConnection) objConnection.Open() End Sub End Module Copyright 2004 Prentice Hall, Inc. 11-64 Executing SQL Statements • • • Visual Basic.NET uses a command object (OleDBCommand) to execute SQL statements. The approach is again similar to that used in Visual Basic 6.0 in that a programmer creates a string memory variable to store the SQL statement to be executed. The SELECT statement is shown in VB.NET Example 11.3. • • REM VB.NET Example 11.3 SELECT emp_last_name, emp_first_name, emp_middle_name, emp_ssn, emp_address, emp_city, emp_state, emp_zip FROM employee WHERE emp_zip = '62025'; Copyright 2004 Prentice Hall, Inc. 11-65 Executing SQL Statements • • • • • The .NET code module named MyConnection shown earlier in VB.NET Example 11.2 needs to be modified to accommodate reading data. The modified code is shown in VB.NET Example 11.4. Note that the strSQL memory variable stores the SELECT command as a series of concatenated character strings. A command object named objCommand is created and the value of strSQL and the objConnection connection object are passed to the objCommand object as parameters inside parentheses. A reader object (objReader) is created to store the actual rows returned when the ExecuteReader method of the objCommand object executes. Copyright 2004 Prentice Hall, Inc. 11-66 Executing SQL Statements • • • • • • • • • • • • • • • • • • • • • • • • REM VB.NET Example 11.4 Module MyConnection Private Const strConnection As String = & _ "Provider = MSDAORA.1; User ID=dbock; Password=mypassword; & _ "Data Source=Company; Persist Security Info=False" Sub Main() Dim strSQL As String strSQL = "SELECT emp_last_name, emp_first_name, " & _ "emp_middle_name, emp_ssn, emp_address, " & _ "emp_city, emp_state, emp_zip " & _ "FROM employee " & _ "WHERE emp_zip = '62025';" Dim objConnection As New _ System.Data.OleDb.OleDbConnection(strConnection) Dim objCommand As New _ System.Data.OleDb.OleDbCommand(strSQL, objConnection) Dim objReader As _ System.Data.OleDB.OleDBReader objConnection.Open() objReader = objCommand.ExecuteReader() 'Additional code goes here to process the rows returned 'by the SQL query. End Sub Copyright 2004 Prentice Hall, Inc. 11-67 End Module Embedding SQL in COBOL Data Division Modifications • • • The Data Division of a COBOL program is used to declare both the structure of files or databases that a program will access. It is also used to declare memory variables known as Working-Storage variables. The Working-Storage Section of a COBOL program is also used to declare tables in memory that will store data rows that are retrieved from database tables. Copyright 2004 Prentice Hall, Inc. 11-68 Embedding SQL in COBOL • • • • • EXEC SQL and END-EXEC commands are used to mark the beginning and end of SQL statements so that a COBOL compiler can properly compile the program. The code in COBOL Example 11.1 shows the declaration of a table named employee that will store data rows retrieved from the employee table of our Company database. This code is located in the Working-Storage Section. You will also note that only the table columns that will be retrieved for processing need to be defined in the table. The other columns in the employee table are ignored. Copyright 2004 Prentice Hall, Inc. 11-69 Embedding SQL in COBOL – – – – – – – – – – – – • • * COBOL Example 11.1 EXEC SQL DECLARE EMPLOYEE TABLE (EMP_SSN CHAR(9), EMP_LAST_NAME CHAR(25), EMP_FIRST_NAME CHAR(25), EMP_MIDDLE_NAME CHAR(25), EMP_ADDRESS CHAR(50), EMP_CITY CHAR(25), EMP_STATE CHAR(2), EMP_ZIP CHAR(9) ) END-EXEC. In order to process the employee table, rows that are retrieved are stored to standard COBOL variables. These are also declared in the Working-Storage Section. Copyright 2004 Prentice Hall, Inc. 11-70 Embedding SQL in COBOL • • • In order to process the employee table, rows that are retrieved are stored to standard COBOL variables. These are also declared in the Working-Storage Section. Row data are moved from the employee table to the COBOL variables. The Working-Storage declaration of these variables is shown in COBOL Example 11.2. – – – – – – – – – – * COBOL Example 11.2 01 EMPLOYEE-WORK. 05 EMP-SSN PIC X(9). 05 EMP-LAST-NAME PIC X(25). 05 EMP-FIRST-NAME PIC X(25). 05 EMP-MIDDLE-NAME PIC X(25). 05 EMP-ADDRESS PIC X(50). 05 EMP-CITY PIC X(25). 05 EMP-STATE PIC X(2). 05 EMP-ZIP PICPrentice X(9). Hall, Inc. Copyright 2004 11-71 Embedding SQL in COBOL • • • • In order to process SQL statements and the employee_data table declared in COBOL Example 11.2, a SQL communications area (SQLCA) must be defined in the server's memory. The SQL communications area includes a SQLCODE parameter. The SQLCODE parameter stores coded values that represent what occurs within an information system whenever any SQL statement executes. The normal execution of an SQL statement causes the SQLCODE parameter to store a value of zero. Program code must be written for the COBOL program Procedure Division in order to test the value of Copyright 2004 Prentice Hall, Inc. 11-72 Contd. Embedding SQL in COBOL • • SQLCODE through the use of IF statements. The IF statements will determine if a given SQL statement executes successfully. The SQL communications area is created by the INCLUDE command shown in COBOL example 11.3. • • • • * COBOL Example 11.3 EXEC SQL INCLUDE SQLCA END-EXEC. Copyright 2004 Prentice Hall, Inc. 11-73 Embedding SQL in COBOL Procedure Division Modifications • The retrieval of data rows through use of an embedded SQL SELECT statement in COBOL requires the storage of data values to host variables. • For the employee table, this simply means that data row values will be stored to the 01 EMPLOYEE-WORK memory variable created in COBOL Example 11.2. • A SELECT statement embedded in a Procedure Division looks like the one shown in COBOL Example 11.4. • Note that the host variables are preceded by a colon ( : ) symbol that is used to differentiate these variables to the program compiler. Copyright 2004 Prentice Hall, Inc. 11-74 Embedding SQL in COBOL • • The SELECT statement is NOT ended by a semicolon when it is embedded in COBOL. The code is located within a paragraph named PROCESS-EMPLOYEE-DATA. – – – – – – – – – – – – * COBOL Example 11.4 PROCESS-EMPLOYEE-DATA. EXEC SQL SELECT EMP_SSN, EMP_LAST_NAME, EMP_FIRST_NAME, EMP_MIDDLE_NAME, EMP_ADDRESS, EMP_CITY, EMP_STATE, EMP_ZIP INTO :EMP-SSN, :EMP-LAST-NAME, :EMP-FIRST-NAME, :EMP-MIDDLE-NAME, :EMP-ADDRESS, :EMP-CITY, :EMP-STATE, :EMP-ZIP FROM EMPLOYEE WHERE EMP_ZIP = "62025" END-EXEC. Contd. Copyright 2004 Prentice Hall, Inc. 11-75 Embedding SQL in COBOL – – – – – – • • IF SQLCODE = 0 * (Place additional code here to process the employee row) ELSE * (Insert additional code here to handle the retrieval * error – no employees with the specified Zip Code) END IF. Additional code would be added to process the data rows retrieved from the employee table by calling the PROCESS-EMPLOYEE-DATA paragraph through use of a standard PERFORM UNTIL command within COBOL. The embedded SQL command replaces the use of a COBOL READ command for the simple retrieval of data. Copyright 2004 Prentice Hall, Inc. 11-76 Embedding SQL in COBOL • • • • Data can be inserted into the employee table by using the SQL INSERT statement in place of the COBOL WRITE command as shown in COBOL Example 11.5. Let's assume that the data values to be inserted have already been moved to the work variables defined within the 01 EMPLOYEE-WORK memory variable created earlier. This could be accomplished by using a series of ACCEPT commands to enable data entry from the keyboard. Alternatively, the data values could be READ from a sequential or indexed data file. Copyright 2004 Prentice Hall, Inc. 11-77 Embedding SQL in COBOL • • • • • • • • • • * COBOL Example 11.5 EXEC SQL INSERT INTO EMPLOYEE (EMP_SSN, EMP_LAST_NAME, EMP_FIRST_NAME, EMP_MIDDLE_NAME, EMP_ADDRESS, EMP_CITY, EMP_STATE, EMP_ZIP) VALUES (:EMP-SSN, :EMP-LAST-NAME, :EMP-FIRSTNAME, :EMP-MIDDLE-NAME, :EMP-ADDRESS, :EMP-CITY, :EMP-STATE, :EMP-ZIP) END-EXEC. Note that the values inserted from the Working-Storage variables match up on a one-for-one basis with the column names defined for the employee table in the Working-Storage Copyright Section of the 2004 Prentice Hall,program. Inc. 11-78